Improve documentation of standalone deriving (c.f. Trac #8851)
Improve documentation of standalone deriving (c.f. Trac #8851)

(cherry picked from commit 9d14262299fe721e49eb0efadebca9d095c834b3)

hferreiro/replay,lukexi/ghc-7.8-arm64,hferreiro/replay,lukexi/ghc-7.8-arm64,hferreiro/replay,lukexi/ghc-7.8-arm64,hferreiro/replay,lukexi/ghc-7.8-arm64,hferreiro/replay,hferreiro/replay,hferreiro/replay,lukexi/ghc-7.8-arm64